A dynamited coral head with dead fish on the edge of Komodo national park, Indonesia. Blast fishing is one of the most destructive fishing practices that takes place in and around the park.
Photograph: Mike Veitch/Alamy

It was the unusual thrashing on the water that caught their attention. As those onboard the dive boat in Indonesia’s Komodo national park drew closer, it became clear it was a green turtle entangled in rubbish and thick fishing net.

The divers managed to lift it out of the water, cut the blue bind from its shell and then set the turtle free, but dive operator Ed Statham says it is just one of the increasing and alarming signs the Unesco heritage site is fast being destroyed.

Each day Statham and his team spot boats illegally fishing inside the protected Coral Triangle area, atop some of the best dive sites in the world.

“It is not just fishing with lines and little boats, it is net fishing, anchoring on dive sites, obvious carcasses lying around, shark finning. And it is happening on a bigger scale than it used to,” explains Statham over the phone from Labuan Bajo.

“If things continue as they are now, Komodo is going to reach a tipping point in the next few years and we are not going to be able to recover.”

A photo taken in February of a dead reef shark missing its top fin. Photograph: Courtesy of Marta Guerra Ramon

Located at the confluence of two oceans, Komodo national park is a series of dramatic hilly islands, home to the famous Komodo dragon, but also a spectacular and diverse marine life, including pelagic fish, manta rays and turtles.

In recent years local dive operators say illegal fishing has become rampant, and while daily park entrance fees were raised almost 500% in 2015 to 175,000 rupiah (£9) – it is now more expensive to dive in Komodo than the Galapagos – the number of marine patrols has only decreased.

On top of that, as word about Komodo spreads, tourism has grown rapidly.

Destructive and illegal fishing combined with unsustainable tourism are putting huge pressure on Komodo’s precious ecosystem. But what happens when a Unesco site is getting destoyed?

Dr Fanny Douvere, coordinator of Unesco’s world heritage marine programme, says there are numerous steps the heritage body can take to help preserve these areas.

Once a site is inscribed as Unesco-heritage listed, it immediately becomes part of a regular evaluation system. If serious problems are detected they are addressed by the world heritage committee, which can include putting a site on its “in danger” list.

The danger listing often helps generate the attention and funding required to rescue a site in critical condition.

There are 29 Unesco marine sites around the world and several are on the danger list, including the Belize Barrier Reef.

In collaboration with Unesco, the government of Belize has adopted new environmental management laws and a protection plan, and introduced a moratorium on offshore drilling.

“Once it is on the danger list there are strict indicators to get off,” explains Douvere.

But there are success stories too. In July last year the Unesco site of Tubbataha reef in the Philippines was designated as a “particularly sensitive sea area”, meaning that large vessels are now required to avoid the area, reducing noise, pollution and future ship groundings.

Aware that Komodo lacks a plan on how to manage its marine environment, the international heritage body sent a team of experts to Komodo last December to start working with local authorities.

Back in Labuan Bajo, the gateway to the national park from the island of Flores, Statham is pushing for urgent action.

He says that when he first arrived in the area as a dive master more than five years ago, the diversity of Komodo “blew his mind” and he is keen to make sure it stays that way.

Thanks to Komodo’s location at the meeting point of two oceans, it is unique in that it does not face the same warming of the seas, and harrowing coral bleaching that many reefs around the world are facing, he says.